Provides the parsing needed for 'rxode2' (Wang, Hallow and James (2016) <doi:10.1002/psp4.12052>). It also provides the 'stan' based advan linear compartment model solutions with gradients (Carpenter et al (2015), <arXiv:1509.07164>) needed in 'nlmixr2' (Fidler et al (2019) <doi:10.1002/psp4.12445>). This split will reduce computational burden of recompiling 'rxode2'.
copied from cf-staging / r-rxode2parse